The last hopes of any British company being involved in building a new generation of nuclear reactors in the UK rest on whether the French state-owned energy group EDF can agree to buy a stake in a large Belgium utility.

Centrica, owner of British Gas, has been in negotiations with EDF for almost four months about buying a 25% stake in British Energy, the nuclear generator bought last autumn by the French group.

Yesterday, Centrica said it had offered its 51% holding in SPE of Belgium in part exchange for the British Energy stake. "The companies expect the discussions to conclude in the next few weeks," it said in a statement. "There can be no certainty that any agreement will be reached."

When EDF agreed to buy British Energy, which had been one of the last independent energy companies left in the UK, it agreed a side deal in principle with Centrica to sell on a 25% stake for £3.1bn. But since then, asset - and power - prices have tumbled as the economy nosedived, and Centrica has been trying to renegotiate.

Since completing the British Energy deal in January, EDF has become exasperated at foot-dragging by Centrica. A part exchange involving the SPE stake is likely to be Centrica's last hope of doing a deal.

EDF has appointed advisers to carry out due diligence on SPE, Belgian's second-largest energy company. Centrica paid €515m last summer to double its stake in SPE but EDF is unlikely to be prepared to pay €1bn (£900m) in total, given the collapse in asset prices since. However, EDF is keen to expand in the Benelux countries and is receptive to the idea of buying the SPE stake. A successful deal would allow both EDF and Centrica to claim they have acquired assets on the cheap.